Seventeen leading US and Canadian retailers have unveiled a five-year plan to improve conditions in factories in Bangladesh that supply high street stores in the west.

Wednesday’s announcement by household names including Walmart and Gap follows a series of accidents in the poor south Asian state, home to the world’s second biggest readymade garment industry.

In April, 1,129 workers were killed when a factory on the outskirts of Dhaka, Bangladesh’s capital, collapsed. Several big western retailers including Primark and Matalan were among its clients. The tragedy provoked a global outcry. It followed a series of smaller incidents over recent years in which hundreds are thought to have died.

US firms have reportedly been reluctant to join any agreements which will be legally binding on participants. Walmart has independently increased factory inspections over recent months.

Funding for the North American plan is based on how much production each retailer has in Bangladesh; those at higher levels will pay $1 million (£670m) a year for five years.

Ten percent of the funds will be set aside to assist workers temporarily displaced by factory improvements or if a factory closes for safety reasons. The money will also support a non-governmental organisation chosen to implement it.

“The safety record of Bangladeshi factories is unacceptable and requires our collective effort,” members of the new scheme, named the Bangladesh Worker Safety Initiative, said in a joint statement. “We can prevent future tragedies by consolidating and amplifying our individual efforts to bring about real and sustained progress.”

However, Jyrki Raina, the general secretary of the IndustriALL global union, said the new agreement was “a pale imitation” of the largely European initiative.

Factory owners have previously expressed concerns that having two different agreements will cause problems.

“If factories are supplying buyers who have signed up to different agreements then what will they follow? We want a unified code of conduct. Everyone needs clarity and the same standards across the industry,” said Mohammed Atiqul Islam, the president of the Bangladesh Garment Manufacturers and Exporters Association.